50pcs Pottery Kiln Nails, Alumina Refractory Ceramic Support Nails High Temperature Resistant Kiln Stilts Cone Clay Firing Studs Reusable Tools Up to 2524℉ (White)

https://a.co/d/0g4fwt6S These work great for risers. Its not a drastic expansion of the flask. Doesn't need to be snug, as long as the lip still touches the surface around the opening, should be good to go.